Switching mechanism

ABSTRACT

A switching mechanism has a member rotatable from an &#39;&#39;off&#39;&#39; position to one or more angular positions in which switch contacts are operated to control the energization of an electric motor driving the clothes drum of a tumbler dryer. The switch contacts may also control the energisation of gas or electric heating elements of the tumbler dryer. A spiral spring is arranged to quickly return the rotatable member to the &#39;&#39;off&#39;&#39; position when a door giving access to the clothes drum is opened, thus de-energizing the electric motor and the heating elements. The rotation of the rotatable member may be arranged to wind a clockwork motor which drives the rotatable member slowly back to the &#39;&#39;off&#39;&#39; position and thus governs the period of energisation of the electric motor. Alternatively the period of energisation may be governed by temperature sensitive switching means arranged to make and break the energising circuit of the electric motor in accordance with the temperature of air heated by the heating means.

Crook et al.

3,823,329 July 9, I974 SWITCHING MECHANISM [75] Inventors: Alan Reginald Crook; Norman Lumsden, both of Peterborough,

Primary Examiner-David Smith, Jr. Attorney, Agent, or F irm-Kirschstein, Kirschstein,

England Ottinger & Frank [73] Assignee: British Domestic Appliances [57] ABSTRACT Peterbomugm England A switching mechanism has a member rotatable from 22 i D 19, 1972 an ofi" position to one or more angular positions in which switch contacts are operated to control the en- [21] APPL 316,507 ergization of an electric motor driving the clothes drum of a tumbler dryer. The switch contacts may also 0 Foreign Application priority Data conttrol energtijatign of gZs or electric heating eleci men s o e um er ryer. spira spring is arrange Dec. 29, 1971 Croat Britain 60619/71 to q y return the rotatable member to the off, p sition when a door giving access to the clothes drum is Opened, thus de energizing the electric motor and the [58 1 Field of Search 200/33 F, 38 A, 61.62, gzf g f g gs g z ig f gl 200/6177 39 A; 34/45 87; 1 83 which drives the rotatable member slowly back to the off position and thus governs the period of'energisa- [56] References Cite-d tion of the electric motor. Alternatively the period of energisation may be governed by temperature sensi- UNITED STATES PATENTS tive switching means arranged to make and break the 2,734,281 2/1956 Kauffman 192/135 i i g ci cuit of the electric motor in accordance 2,759,485 8/1956 Guth g 200/6l.62 with the temperature f i heated by the heating 2,946,902 7/l960 Hagen 200/38 F means 3,088,221 5/1963 Pansing et al.... 3,109,717 11/1963 Clapp 34/45 18 Claims, 7 Drawing Figures 11 6 T 10 14 4 I 9 12 2 I BEBE-Ir:

PATENTED JUL 91974 SHEET 1 OF 4 PATENTED L 91974 SHEET 2 BF 4 PATENTEDJUL w I 3,823 329 sum 3 BF 4 PAIENTEDJUL 91914 SHEET Q BF 4 {Kin 3 M P} H I Ann B c A A 4 .0 5 6 C 1 SWITCHING MECHANISM This invention relates to switching mechanisms suitable for controlling the operation of an apparatus having a rotatable drum which is driven by an electric motor and which is reached through an access door in the casing of the apparatus. With such apparatus it is desirable that the electric motor which drives the drum should be switched off when the access door is opened, so that rotation of the drum is discontinued.

According to one aspect of the present invention a switching mechanism includes a member rotatable from an off position to one or' more angular positions to cause operation of switching means for energising an electric motorarranged to drive a rotatable drum, rotation of the rotatable member to the or each angular position being arranged to govern the duration of the energisation of the electric motor, and spring means arranged to apply torque to the rotatable member such as to return the rotatable member quickly to the off position and thus terminate the period of energisation, the spring means being restrained from applying torque to the rotatable member by latch means which is re leased when a door giving access to the drum is opened.

Rotation of the rotatable member to an angular position may be arranged to wind a clockwork motor which, when wound, drives the rotatable member slowly back to the off. position andv thus determines the duration of the energisation of the electric motor. I

The rotatable member may be arranged to be rotatable to a plurality of different predetermined angular positions, in each of which the clockwork motor is wound to a different predetermined extent and thustakes a different predetermined time-to return the rotatable member to the off position.

The latch means may be arranged to engage and restrain a stepped member to which the torque is applied by the spring means, the release of the stepped member by the latch means allowing the spring means to apply the torque to the rotatable member after a predetermined angular rotation of the stepped member relative to the rotatable member.

The invention may be advantageously applied to a tumbler clothes dryer in which the rotatable drum is perforated so that heated air can be passed through the perforations to dry the clothes contained in the drum,

the air being heated by suitable heating means such as electric heating elements or gas. With a tumbler clothes dryer it is desirable that the heating means which heats the air should be prevented from functioning while the access door remains open. To this end further switching contacts operated by the rotatable member may be arranged to control the energisation of electric heating elements or control the operation of solenoid operated valves through which gas is supplied to gas heatingmeans.

When the invention is applied to a tumbler clothes dryer the duration of the energisation of the electric When the duration of the energisation of the electric motor is governed by a clockwork motor, the slow return of the rotatablemember to the off position by the clockwork motor may be delayed by a further latch means arranged to be released when the exhaust air from the clothes dryer attains a predetermined temperature.

Preferably the further latch means is arranged to engage and restrain a stepped cam rotationally fast with the rotatable member, and to be released by temperature responsive means such as an expansible bellows device connected hydraulically with a temperature sensing phial through a capillary tube. A plurality of stepped portions may be provided on the stepped cam, each stepped portion corresponding to a different predetermined temperature at which the further latch means is to be released.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: I

FIG. I is a diagrammatic view of a switching mechanism embodying the invention and incorporated in an electric tumbler clothes dryer;

FIG. 2 is a section on the line lI--II in FIG. 1 but drawn to a larger scale than that Figure;

FIG. 3 is a diagrammatic view of a modified form of the switching mechanism shown in FIG. 1;

FIG. 4 is a section on the line IV-IV in FIG. 3 but drawn to a larger scale than that Figure;

FIG. 5 is a diagrammatic view of another form of switching mechanism in accordance with the invention incorporated in an electric tumbler clothes dryer;

FIG. 6 is a section on the line VI-VI in FIG. 5 but drawn to a larger scale than that Figure; and

FIG. 7 is a schematic circuit diagram relating to the switching mechanism shown in FIG. 5.

Referring in the first instance to FIGS. 1 and 2, the switching mechanism comprises a frame 1 which forms part of the casing of the electric tumbler clothes dryer and in which is rotatably mounted a spindle 2. Mounted on a side 3 of the frame I is a clockwork timer motor 4 through which the spindle 2 passes, the spindle 2 being rotatable to wind up the clockwork motor 4 by a control knob 5 secured to one end. Mounted on a side 6 of the frame I is a plurality of snap action switches 7 each of which is arranged to be operated by an associated cam 8 mounted on the spindle 2. The snap action switches 7 form part of the electrical control circuit of the tumbler clothes dryer.

Rotatably mounted on the spindle 2, so that they are rotatable together, are a cylindrical collar 9 and a circular disc 10 having a plurality of steps ill circumferentially spaced around its periphery. Conveniently, the collar 9 and the disc 10 are formed in one piece from a suitable plastics material by a moulding operation. The collar 9 is provided with an axially extending lug 12 which can engage a pin 13 extending radially from an adjacent part of the spindle 2 when the collar 9 and disc 10 are rotated relative to the spindle 2. A spiral spring 14 mounted on the collar 9 has its inner end secured to the collar 9 and its outer end anchored to the casing at a convenientposition (not shown).

Pivotally mounted between the sides 3 and 6 of the frame I is a latching lever 15 which carries an upturned projection 16 arranged to engage a selected one of the steps ll on the disc 10, depending on the angular position of the disc 10. Pivotal movement of the latching lever 15 against pressure exerted by a return spring 117 is controlled by the inner'wire l8 of a Bowden cable 19 which is actuated by the opening and closing of an access door (not shown) of the tumbler clothes dryer.

The switching mechanism functions in the following manner as a variable timer which can select and control drying operations of different predetermined durations. Clothes which are to be dried are loaded into a clothes drum (not shown) and the access door is closed. The control knob is then rotated so that the spindle 2 rotates relative to the collar 9 and the pin 13 engages the lug 12. The collar 9 and the disc rotate with the spindle 2 and wind up the spiral return spring 14. Rotation of the spindle 2 also winds'up the clockwork timer motor 4 to an extent determined by the angular rotation of the control knob 5. The control knob 5 is suitably calibrated so that it can be set at any-one of a plurality of, say four, predetermined positions each of which corresponds to a position in which the projection 16 on the latching lever engages one of the steps 11 on the disc 10. Rotation of the spindle 2 also rotates the cams 8 and thus actuates the snap action switches 7 in a predetermined sequence to control the energisation of an electric motor (not shown) for rotating the clothes drum of the tumbler clothes dryer and also to control the energisation of electric heating elements (not shown) which heat the air passing through the clothes drum.

. When the control knob 5 has been set to one of the predetermined positions and the projection 16 is engaging a step 11 on the disc 10, the clockwork motor 4 drives the spindle 2 slowly back to its original position, the time taken to reach the original position being say ten minutes, twenty minutes or thirty minutes, depending on the angular position to which the knob 5 was rotated. During this time the disc 10 and the collar 9 are held stationary by the projection 16 on the latching lever 15 despite the torque applied by the spiral spring 14. As the spindle 2 rotates towards its original position the switches 7 are operated in sequence by the cams 8 to control the duration of the energisation of the electric motor driving the drum of the tumbler clothes dryer and the duration of the energisation of the heating elements.

Should the access door of the tumbler clothes dryer be opened during this period, a pull is exerted on the inner wire 18 of the Bowden cable 19, causing the latching lever 15 to pivot so that the projection 16 is moved clear of the step 11. The torque exerted by the spiral spring 14 rapidly rotates the disc 10 and the collar 9 until the lug 12 on the collar 9 engages the pin 13 and rapidly rotates the spindle 2 to its original position, the torque of the spiral spring being sufficient to override the clockwork motor 4. The cams 8 rotate with the spindle 2 so that the switches 7 are rapidly operated to de-energise the heating elements and the electric motor driving the drum of the tumbler clothes dryer, thus'reducing the hazard to anyone inserting or removing clothes through the open door. Moreover, closing the door will not result in theheating elements or the motor being energised inadvertently, since the door must be closed and the control knob 5 set to one of its predetermined positions before the operation of the tumbler dryer is resumed. It is envisaged that the first step on the disc 10 would provide a cool, non-heated, drying operation of predetermined duration, while the subsequent steps would provide longer, heated, drying operations. Other controlled functions may be obtained by providing additional switches 7 and associated cams 8, and by selectively energising a plurality of heating elements.

Referring now to FIGS. 3 and 4, the modified form of switching mechanism comprises a frame 21 in which is rotatably mounted a spindle 22 and on a side 23 of which is mounted a clockwork timer motor 24 through which the spindle 22 passes. The spindle 22 is rotatable by a control knob 25 to wind up the clockwork motor 24. Mounted on a side 26 of the frame 21 is a plurality of snap action switches 27 each of which is arranged to be operated by an associated cam 28 mounted on the spindle 22. The snap action switches 27 form part of an electrical control circuit of the tumbler clothes dryer.

Rotatably mounted on the spindle 22 is a cylindrical collar 29 and a circular disc 30 having a plurality of steps 31 circumferentially spaced around its periphery. Conveniently, the collar 29 and the disc 30 are formed in one piece from a suitable plastics material. The collar 29 is provided with an axially extending lug 32 arranged to engage a pin 33 which extends radially from an adjacent part of the spindle 22 when the collar 29 and the disc 30 are rotated relative to the spindle 22. A spiral spring 34 mounted on the collar 29 adjacent the disc 30 has its inner end secured to the collar 29 and its outer end anchored to the casing at a convenient position (not shown)v A further collar 35 carrying a stepped cam 36 is secured to the spindle 22 by a pin 37 Pivotally mounted between the sides 23 and 26 of the frame 21 is a latching lever 38 which carries an upturned projection 39 arranged to engage a selected one of the steps 31 on the disc 30, depending on the angular position of the disc 30. A further upturned projection 40 on the latching lever 38 is arranged to engage one of a plurality of stepped portions 41A, 41B, 41C and 418 on the cam 36. A temperature sensing phial 42, which is located so as to monitor the temperature of the air exhausted from the tumbler dryer, is hydraulically connected by a capillary tube 43 to an associated bellows device 44 mounted on the frame 21 so that its extensible tip 45 engages the latching lever 38. The bellows device 44 is arranged so that an increase in the temperature of the exhaust air impinging on the phial 42 expands the bellows device 44 and moves the latching lever 38 in a direction such as to disengage the projection 40 from a stepped portion 41 of the cam 36. Pivotal movement of the latching lever 38 against pressure exerted by a return spring 46 can also be brought about by the inner wire 47 of a Bowden cable 48 which is actuated by the opening and closing of an access door (not shown) of the tumbler clothes dryer.

The switching mechanism shown in FIGS. 3 and 4 has settings corresponding to say three programmes of operations for the tumbler clothes dryer, to cater for example for, (A) a small load of delicate fabrics, (B) a medium load of heavy linens or (C) a large load of heavy linens. The different temperature settings required for these loads are provided automatically by the different heights of the stepped portions 41A, 41B and 41C of the cam 36. For example, if a medium load of heavy linens is to be dried, the control knob 25 is set to the position in which the projection 40 on the latching lever 38 engages the stepped portion 418 and the projection 39 engages a corresponding step 31 on the circular disc 30. The projection 40 holds the cam 36 in the selected position so that the collar 35 prevents the spindle 22 from being rotated by the timer motor 24 until the exhaust air has been heated to the required temperature. When the exhaust air impinging on the phial 42 attains the required temperature, the bellows device 44 engages the latching lever 38 and moves the projection 40 clear of the stepped portion 413, allowing the timer motor 24 to drive the spindle 22 back to its original position so that the cams 28 operate the switches 27. During this time the disc 30 and the collar 29 are held stationary by the projection 39 on the latching lever 38 despite the torque applied by the spiral spring 34.

Should the access door of the tumbler clothes dryer be opened at any time during the drying programme, a pull is exerted on the inner wire 47 of the Bowden cable 48, causing the latching lever 38 to pivot so that the projection 39 is moved clear of the step 31 on the'disc 30. The torque exerted by the spiral spring 34 rapidly rotates the disc 30 and the collar 29 until the lug 32 engages the pin 33 and rapidly rotates the spindle 22, the torque of the spiral spring 34 being sufficient to override the clockwork motor 24. The cams 28 rotate with the spindle 22 so that the switches 27 are rapidly operated to de-energise the heating elements and the electric motor driving the drum of the clothes dryer, thus reducing the hazard to anyone inserting or removing clothes through the open door. Moreover, as with the switching mechanism shown in FIGS. 1 and 2, closing the access door will not result in the heating element or the electric motor being energised inadvertently, since the access door must be closed and the control knob 25 set to one of itspredetermined positions before the operation of the tumbler dryer is resumed.

It will be appreciated that the height of the stepped portions 4lA, 41B, and 41C vary, so that a much greater movement of the bellows device 44 is required to move the projection 40 clear of the stepped portion 41C than is required to move the projection clear of the stepped portion 4lA. Therefore the temperature attained by the exhaust air before the projection 40 is moved clear of the stepped portion 41C to allow the clockwork motor 24 to drive the spindle is much higher than the temperature attained before the projection 40 is moved clear of the stepped portion 418 and the clockwork motor 24 is allowed to drive the spindle 22. Similarly the temperature at which the projection 40 is moved clear of the stepped portion 41A is much lower than the temperature at which the projection 40 is moved clear of the stepped portion 41B. The stepped portion 418 is the start or off position to which the switch mechanism is returned by the spiral spring 34 when the access door is opened.

Referring now to H68. 5 to 7, the switching mechanism comprises a frame 511 which forms part of the easing of the electric tumbler clothes dryer and in which is rotatably mounted a spindle 52. Mounted on a side 53 of the frame 51 is a plurality of snap action switches 54A, 54B and 54C, each of which is arranged to be operated by an associatedcam 55 mounted on the spindle 52. The snap action switches form part of the electrical control circuit of the tumbler clothes dryer (see FIG. 7), in which switch 54A is connected to the Line side of an A.C. supply 58. The switch 54A is shown as a single pole ON/OF F switch, but if required it may be a double pole switch with the other pole connected to the Neutral side of the A.C. supply 50. Switch 548 is con nected in the supply circuit of an electric motor 56 arranged to drive the clothes drum 57 of the clothes dryer. Switch 54C is connected in the supply circuit of an electric heating element 58 arranged to heat air passing through the clothes drum 57. A door 59 giving access to the clothes drum 57 is provided with a mechanical linkage 68 arranged so that the opening of the door 59 opens the switch 54A.

A thermostat 6ll, having a temperature sensing phial 62 located so as to monitor the temperature of the air exhausted from the tumbler dryer, is connected to the switches 54B and 54C by a mechanical linkage 63 and arranged so that the switches 54B and 54C are closed at ambient temperature. A further thermostat 64 is connected in the supply circuit of the electric motor 56 and is arranged so that if the temperature of the air exhausted from the tumbler dryer rises 30 40 F above ambient temperature, contacts of the thermostat 64 close and provide a short-circuit across switch 54B.

Mounted on the spindle 52 and secured to it by a pin 66, are a cylindrical collar 67 and a cam 68 having a plurality of stepped portions 69V, 69W, 69X, 69Y and 692' circumferentially spaced around its periphery. Conveniently, the collar 67 and the cam 68 are formed .in one piece from a suitable plastics material by a moulding operation. A spiral spring 70 mounted on the collar 67 has its inner end secured to the collar 67 and its outer end anchored to the casing at a convenient position (not shown).

Pivotally mounted between the sides of the frame 51 is a latching lever 71 which carries an upturned projection 72 arranged to engage a selected one of the stepped portions on the cam 68, depending on the angular position to which the cam 68 has been set by a control knob 65 secured to the spindle 52. A temperature sensing phial 73, which is located so as to monitor the temperature of the air exhausted from the tumbler dryer, is hydraulically connected by a capillary tube 74 to an associated bellows device 75 mounted on the frame 51 so that its extensible tip 76 engages the latching lever 71, these elements corresponding in part to those represented at 61 and 63 of the circuit of FIG. 7. The bellows device 75 is arranged so that an increase in the temperature of the exhaust air impinging on the phial 73 expands the bellows device 75 and moves the latching lever 71 in a direction such as to disengage the projection 72 from a stepped portion of the cam 68. Pivotal movement of the latching lever 71 against pres sure exerted by a return spring 77 can also be brought about by the inner wire 78 of a Bowden cable 79 which is actuatedby the opening and closing of the access door 59 of the tumbler clothes dryer, and which forms part of the mechanical linkage shown schematically at 60 in FIG. 7.

The switching mechanism shown in FIGS. 5 to 7 has settings corresponding to say three programmes of operations for the tumbler clothes dryer, to cater for example for, (X) a small load of delicate fabrics, (Y)

a medium load of heavy linens or (Z) a large load of heavy linens. Thedifferent temperature settings re quired for these loads are provided automatically by the different heights of the stepped portions 69X, 69Y and 69Z of the cam 68. The stepped portion 69W provides a cool position in which the heating element 58 is de-energised. For example, if a medium load of heavy linens is to be dried, the load is first placed in the clothes drum 57 through the access door 59, the control knob 65 being in the off position so that the electric motor 56 and the heating element 58 are deenergised and the contacts of the thermostat 64 are open. The drying operation is started by turning the control knob 65 to the position in which the projection 72 on the latching lever 71 engages the stepped portion 69Y on the cam 68 and then closing the door 59. These actions may be carried out in reverse order. Turning the control knob 65 to this position causes the cams 55 to operate switches 54A, 54B and 54C so that the electric motor 56 and the heating element 58 are energised. The projection 72 holds the cam 68 in the selected position and prevents the spindle 52 from being rotated by the spiral spring 70.

As the temperature of the exhaust air rises to about 40 F above ambient temperature the contacts of the thermostat 64 close and provide a short circuit across the switch 54B. When the exhaust air impinging on the phial 73 attains the required temperature, the bellows device 75 engages the latching lever 71 and moves the projection 72 clear of the stepped portion 69Y, allowing the spiral spring 70 to drive the spindle 52 to a cool position in which the projection 72 engages the stepped portion 69 W on the cam .68. When the spindle 52 is rotated to this position the cams 55 open the switches 54B and 54C so that the heating element 58 is de-energised, but the electric motor 56 continues to run due to the short-circuit provided by the thermostat 64. The temperature of the exhaust air begins to fall until eventually the contacts of the thermostat 64 are opened and the short circuit is removed from switch 54B so that the electric motor 56 is de-energised. The control knob 65 remains in the cool position until either the door 59 is opened or the control knob is turned manually to another position.

Should the access door 59 of the tumbler clothes dryer be opened at any time during the drying programme, a pull is exerted on the inner wire 78 of the Bowden cable 79, causing the latching lever 71 to pivot so that the projection 72 is moved clear of the stepped portion on the cam 68. The torque exerted by the spiral spring 70 rapidly rotates the cam 68, the collar 67 and the spindle 52 so that they return to the off position in which the'projection 72 engages the stepped portion 69V on the cam 68. The cams 55 rotate with the spindle 52 so that the switches 54A, 54B and 54C are all rapidly operated to de-energise the heating element 58 and the electric motor 56, thus reducing the hazard to anyone inserting or removing clothes through the open door 59. Moreover, as with the switching mechanism shown in FIGS. 1 and 2, closing the access door 59 will not result in the heating element 58 or the electric motor 56 being energised inadvertently, since the access door 59 must be closed and the control knob 65 set to one of its predetermined positions before the operation of the tumbler dryer is resumed.

Although in the embodiments of the invention described above the air is heated by electric heating elements, in other embodiments of the invention the air may be heated by a suitable gas heater and the supply of gas to this heater may be controlled by solenoid operated valves.

We claim:

1. A switching mechanism for energising an electric motor arranged to drive a rotatable drum including:

a. a member rotatable from an off position to one or more angular positions to cause operation of switching means for energising the electric motor,

d. releasing means for releasing the latch means when a door giving access to the drum is opened, so that the spring means applies torque to the rotatable member.

2. A mechanism as claimed in claim 1, wherein the I latch means is arranged to engage and restrain a stepped member to which torque is applied by the spring means, and the release of the latch means by the latch releasing means allows the stepped member to apply the torque to the rotatable member after a predetermined angular rotation of the stepped member relative to the rotatable member.

3. A mechanism as claimed'in claim 1, wherein the rotation of the rotatable member to an angular position is arranged to wind a clockwork motor which, when wound, drives the rotatable member slowly back to the off position and thus determines the duration of the energisation of the electric motor.

4. A mechanism as claimed in claim 3, wherein the rotatable member is arranged to be rotatable to a plurality of different predetermined angular positions, in each of which the clockwork motor is wound to a different predetermined extent and thus takes a different predetermined time to slowly return the rotatable member to the off position.

5. A mechanism as claimed in claim 3, wherein the slow return of the rotatable member by the clockwork motor is delayed by further latch means arranged to be released when air passing through the drum attains a predetermined temperature.

6. A mechanism as claimed in claim 5, wherein the further latch means is arranged to engage and restrain a stepped cam rotationally fast with the rotatable member and to be released by temperature responsive means when the air passing through the drum reaches the predetermined temperature.

7. A mechanism as claimed in claim 6, wherein the stepped cam is provided with a plurality of stepped portions each corresponding to a different predetermined temperature at which release by the further latch means is efiected.

8. A mechanism as claimed in claim 6, wherein the temperature responsive means includes expansible bellows means hydraulically connected with a temperature sensing phial through a capillary tube.

9. A mechanism as claimed in claim 1, wherein the duration of the energisation of the electric motor is determined by temperature responsive means arranged to respond to the temperature of air heated by heating means.

10. A mechanism as claimed in claim 9, wherein the rotation of the rotatable member to an angular position energises the heating means so that the temperature responsive means starts reckoning the period of energisation of the motor, and the spring means is arranged to return the rotatable member to a further angular position adjacent the off position after a time detemiined by the rising temperature of the heated air, the return of the rotatable member to the further angular position de-energising the heating means so that the temperature responsive means bring about de-energisation of the electric motor when the temperature of the air has fallen to a predetermined value.

11. A mechanism as claimed in claim 10, wherein the latch means is arranged to engage and restrain a stepped cam rotationally fast with the rotatable member and to be released by the temperature responsive means when the air rises to a predetermined temperature and thus allow the rotatable member to return to the further angular position at which the latch means again engages the stepped cam.

12. A mechanism as claimed in claim 11, wherein the stepped cam is provided with a plurality of stepped portions each corresponding to a different predetermined temperature at which the return of the rotatable member to the further angular position can be effected.

' 13. A mechanism as claimed in claim 11, wherein the temperature responsive means includes expansible bel lows means adapted to release the latch means when energisation of heating M) the air reaches a predetermined temperature and allow the rotatable member to return to the further angular position.

14. A mechanism as claimed in claim 13, wherein the expansible bellows means is hydraulically connected with a temperature sensing phial through a capillary tube.

15. A mechanism as claimed in claim 9, wherein the heating means comprises one or more electric heating elements to which the supply of energising current is controlled by switch means.

16. A mechanism as claimed in claim 9, wherein the heating means is a gas heater to which the supply of gas is controlled by solenoid operated valves.

17. A tumbler clothes dryer incorporating a switching mechanism as claimed in claim 1.

18. A tumbler clothes dryer incorporating a switching mechanism as claimed in claim 1, wherein the release of the spring means by the latch means when the access door is opened is arranged to bring about demeans of the tumbler dryer. l 

1. A switching mechanism for energising an electric motor arranged to drive a rotatable drum including: a. a member rotatable from an ''off'' position to one or more angular positions to cause operation of switching means for energising the electric motor, the rotation of the rotatable member to the or each angular position being arranged to govern the duration of the energisation of the electric motor; b. spring means arranged to apply torque to the rotatable member such as to return the rotatable member quickly to the ''off'' position and thus terminate the period of energisation; c. latch means arranged to prevent the spring means from applying torque to the rotatable member; and d. releasing means for releasing the latch means when a door giving access to the drum is opened, so that the spring means applies torque to the rotatable member.
 2. A mechanism as claimed in claim 1, wherein the latch means is arranged to engage and restrain a stepped member to which torque is applied by the spring means, and the release of the latch means by the latch releasing means allows the stepped member to apply the torque to the rotatable member after a predetermined angular rotation of the stepped member relative to the rotatable member.
 3. A mechanism as claimed in claim 1, wherein the rotation of the rotatable member to an angular position is arranged to wind a clockwork motor which, when wound, drives the rotatable member slowly back to the ''off'' position and thus determines the duration of the energisation of the electric motor.
 4. A mechanism as claimed in claim 3, wherein the rotatable member is arranged to be rotatable to a plurality of different predetermined angular positions, in each of which the clockwork motor is wound to a different predetermined extent and thus takes a different predetermined time to slowly return the rotatable member to the ''off'' position.
 5. A mechanism as claimed in claim 3, wherein the slow return of the rotatable member by the clockwork motor is delayed by further latch means arranged to be released when air passing through the drum attains a predetermined temperature.
 6. A mechanism as claimed in claim 5, wherein the further latch means is arranged to engage and restrain a stepped cam rotationally fast with the rotatable member and to be released by temperature responsive means when the air passing through the drum reaches the predetermined temperature.
 7. A mechanism as claimed in claim 6, wherein the stepped cam is provided with a plurality of stepped portions each corresponding to a different predetermined temperature at which release by the further latch means is effected.
 8. A mechanism as claimed in claim 6, wherein the temperature responsive means includes expansible bellows means hydraulically connected with a temperature sensing phial through a capillary tube.
 9. A mechanism as claimed in claim 1, wherein the duration of the energisation of the electric motor is determined by temperature responsive means arranged to respond to the temperature of air heated by heating means.
 10. A mechanism as claimed in claim 9, wherein the rotation of the rotatable member to an angular position energises the heating means so that the temperature responsive means starts reckoning the period of energisation of the motor, and the spring means is arranged to return the rotatable member to a further angular position adjacent the ''off'' position after a time determined by the rising temperature of the heated air, the return of the rotatable member to the further angular position de-energising the heating means so that the temperature responsive means bring about de-energisation of the electric motor when the temperature of the air has fallen to a predetermined value.
 11. A mechanism as claimed in claim 10, wherein the latch means is arranged to engage and restrain a stepped cam rotationally fast with the rotatable member and to be released by the temperature responsive means when the air rises to a predetermined temperature and thus allow the rotatable member to return to the further angular position at which the latch means again engages the stepped cam.
 12. A mechanism as claimed in claim 11, wherein the stepped cam is provided with a plurality of stepped portions each corresponding to a different predetermined temperature at which the return of the rotatable member to the further angular position can be effected.
 13. A mechanism as claimed in claim 11, wherein the temperature responsive means includes expansible bellows means adapted to release the latch means when the air reaches a predetermined temperature and allow the rotatable member to return to the further angular position.
 14. A mechanism as claimed in claim 13, wherein the expansible bellows means is hydraulically connected with a temperature sensing phial through a capillary tube.
 15. A mechanism as claimed in claim 9, wherein the heating means comprises one or more electric heating elements to which the supply of energising current is controlled by switch means.
 16. A mechanism as claimed in claim 9, wherein the heating means is a gas heater to which the supply of gas is controlled by solenoid operated valves.
 17. A tumbler clothes dryer incorporating a switching mechanism as claimed in claim
 1. 18. A tumbler clothes dryer incorporating a switching mechanism as claimed in claim 1, wherein the release of the spring means by the latch means when the access door is opened is arranged to bring about de-energisation of heating means of the tumbler dryer. 